Cancer is one of the leading causes of death in the United States, accounting for about 25 percent of all deaths. Since the mid-1970s, the survival rate of cancer on average has increased from about 50 percent to over 60 percent, reflecting improvements in treatment and diagnosis at earlier stages of cancer. However, there are differences in the survival rates of varying types of cancer. More specifically, patients with metastatic cancer have significantly lower odds of survival. For example, the 5-year relative survival for localized breast cancer is about 98 percent today; however, that rate drops to 26 percent for women with metastatic breast cancer (American Cancer Society Cancer Facts & Figures 2007. Atlanta: American Cancer Society; 2007; herein incorporated by reference in its entirety). Thus, the development of new tools for early metastatic cancer detection is critical for improving the odds of survival for many cancer patients. Metastatic tumors have been shown to have elevated levels of enzymes, such as matrix metalloproteinsase-7 (MMP-7), that break down tissues in the body. Since these enzymes are present at high levels, they have the potential to become targets for anticancer imaging and diagnostic techniques.
Matrix metalloproteinases (MMPs) are a family of zinc containing enzymes that mediate the breakdown of connective tissues (Whittaker et al., Chemical Reviews 1999, 99:2735-2776; herein incorporated by reference in its entirety). MMPs are important in many physiological processes including wound healing, bone resorption, and uterine and breast involution (Mullins and Rohrlich, Biochim and Biophys Acta 1983, 695.177-214; herein incorporated by reference in its entirety). The enzymes are generally expressed at low levels, but these levels rise rapidly during inflammation, wound healing, and cancer (Coussens et al., Science 2002, 295:2387-2392; herein incorporated by reference in its entirety). Overexpression of MMPs has been linked to several degenerative diseases such as multiple sclerosis (Rosenberg, et al., Neurology 1996, 46:1626-1632., Chandler, et al., Neuroscience Letter 1995, 201:223-226., Proost et al., Biochemical and Biophysical Research Communications 1993, 192:1175-1181., Gijbels et al., Journal of Cellular Biochemistry (Supplement) 1994, 18D, 143.; herein incorporated by reference in their entireties), corneal ulceration (Hook, et al., Investigative Opthalmology 1973, 12:771-776.; herein incorporated by reference in its entirety), periodontal disease (Golub et al., Journal of the American Dental Association 1994, 125:163-171.; herein incorporated by reference in its entirety), gastrointestinal ulceration (Saarialho-Kere et al., American Journal of Pathology 1996, 148:519-526.; herein incorporated by reference in its entirety), abdominal aortic aneurysm (Thompson et al., Annals of the New York Academy of Sciences 1996, 800: 157-174.; herein incorporated by reference in its entirety), rheumatoid arthritis (Cawston, T E, Pharmacology & Therapeutics 1996, 70:163-182.; herein incorporated by reference in its entirety), osteoarthritis (Cawston, T E, Pharmacology & Therapeutics 1996, 70:163-182., O'Byme et al., Inflammation Research 1995, 44:S 117-S118; herein incorporated by reference in their entireties), cancer invasion (Edwards and Murphy, Nature 1998, 394:527-528., Kataoka et al., American Journal of Pathology 1999, 154:457-468., Brabletz et al., American Journal of Pathology 1999, 155:1033-1038., Noe et al., Cell Science 2001, 114:111-118.; herein incorporated by reference in their entireties), and tumor metastasis (Aparicio et al., Carcinogenesis 1999, 20:1445-1451., Lampert et al., American Journal of Pathology 1998, 153:429-437., Zucker et al., American Journal of Pathology 2001, 158:1921-1928., Zeng et al., Clinical Cancel Research 2002, 8:144-148., Chambers et al., Journal of the National Cancer Institute 1997, 89:1260-1270.; herein incorporated by reference in their entireties). As early as 1949 MMPs were recognized as depolymerizing enzymes that were believed to facilitate tumor growth by degrading connective tissues (Gersh and Catchpole, American Journal of Anatomy 1949, 85:457-521.; herein incorporated by reference in its entirety). Recently, the mechanistic role of MMPs in tumor metastasis and invasion has been shown to be much more complex than previously thought. However, the positive correlation between MMP expression levels and the invasive potential of a tumor remains. The detection of MMP is critical for identifying metastatic cancer and could be used to monitor the efficacy of MMP inhibitors, leading to the optimization of anti-cancer therapeutic protocols (Zucker and Cao, Nature Medicine 2001, 7:655-656., Coussens et al., Science 2002, 295:2387-2392., Nelson et al., Journal of Medical Oncology 2000, 18:1135-1149.; herein incorporated by reference in their entireties). The current method of monitoring MMP activity consists of ex vivo assays on excised tissues or fluid samples. In order to detect MMP activity in vitro, fluorescent probes have been developed including ultraviolet-visible and near-infrared probes and proteolytic beacons (Stack and Gray, Journal of Biological Chemistry 1989, 264:4277-4281., Netzel-Arnett et al., Analytical Biochemistry 1991, 195:86-92.; herein incorporated by reference in their entireties). The practical applications of fluorescence techniques are restricted to the observation of cells, small animals, and tumors near the surface of the skin due to the limited penetration of light (<10 mm). Thus, there has been a need to develop techniques for MMP detection that are more applicable to humans (Coussens et al., Science 2002, 295:2387-92., Nelson et al., Journal of Clinical Oncology 2000, 18:1135-1149.; herein incorporated by reference in their entireties). MRI provides an alternative to light microscopy, allowing the noninvasive, in vivo imaging of opaque organisms in three dimensions at millimeter resolution (Louie et al., Nature Biotechnology 2000, 18:321-325.; herein incorporated by reference in its entirety).
MRI has become a popular technique for noninvasive imaging of opaque specimens due to its high spatial and temporal resolution. In MRI, images are acquired by employing radio frequency pulses to excite nuclear spins of a specimen. The observed signal is from the protons of water molecules in the specimen. MRI generates 3-D images due to intrinsic variations in water proton concentrations in different tissues. Whereas optical microscopy is limited by light scattering, MRI can image in three dimensions with high spatial and temporal resolution. Exogenous agents can be used manipulate relaxation times (T1 and/or T2) of water protons within a sample and enhance contrast in the image. Principle limitations to current agents are amplification of signal, in vivo delivery, lack of multimodal validation, and the absence of biochemical reporters. Improved systems are needed to expand imaging capabilities.